The specific objectives for the period of requested support are: 1) to define the active site on insulin, 2) to locate the site or sites of insulin binding in tissues, 3) to define the intermolecular interactions between insulin and tissue receptors and, 4) to study the mechanisms by which insulin causes its various actions. We feel that in order to accomplish these objectives that the most reliable initial approach is to define the intramolecular and intermolecular interactions of insulin that are related to the biological activity or activities of insulin. We feel this way because the precise structure of insulin is now known and we are convinced that these parameters are at the present time the most valid available criteria that will yield information valuable in accomplishing the major objectives of this proposal. The approaches to be employed in arriving at the objectives of this project can best be divided into three areas: 1) the studies concerned with the structure-function relations of insulin in solution, 2) the studies concerned with use of purified insulin antibodies in vitro and in vivo, and 3) the studies concerned with the localization of insulin in tissues. It should be emphasized that these areas are interrelated. The subdivisions are arbitrarily being employed only to clarify the overall approach to obtain our objectives. BIBLIOGRAPHIC REFERENCES: Sodoyez, J. C., Goffaux-Sodoyez, F., Zimmerman, A.E. and Arquilla, E. R.: I127 or Carrier Free I125 Monoiodoinsulin. Preparation, Physical, Immunological, and Biological Properties, and Susceptibility to "Insulinase" Degradation. J. of Biol. Chem. 250:4268-4277, 1975.